1. Field of the Invention
This invention relates to a method for manufacturing a spectacle-glass for myopes, whereby one starts from a semi-finished glass, that is a glass which has on the inner side, a slight concave hollowing.
2. Discussion of the Prior Art
Myopes with severe eye divergences and with a requirement for high diopter values, have up to now always been helped with glasses which always have a thick edge thickness. The disadvantages thereof are clear: the glasses are unaesthetic; the frame selection is limited; the glasses are heavy and make the spectacles uselessly heavier. Moreover these conditions influence the field of view due to forming disturbing concentric circles resulting from the light refraction in the glasses.
It has already been proposed to lower the glass edge thickness. In spite of the techniques being used, the edge thickness lowering had a detrimental action on the field of view or on the aesthetic appearance.
Such an example lies in the technique as described in the Swiss Pat. No. 634,928 in the name of W. Wrobel, whereby there may be obtained but a field of view which is markedly narrower than the optimum field of view required in relation with the diopter value.
A search was also made for solutions which optimize the field of view as well as they satisfy the requirements from the aesthetic point of view. Belgian Pat. No. 899,955 filed on June 19, 1984 in the name of the Applicant, comprises an attempt in such a direction. According to said Patent, the optimum field of view is obtained or retained with a marked lowering from 40 to 51% of the edge thickness and a convex finishing of the transition between the center concave hollowing of the spectacle-glass and the flat milled edge.
There was obtained hereby the object of an optimum field of view together with still a substantial improvement from the aesthetic point of view, that is an already strongly lowered edge thickness and avoiding the aesthetically-disturbing bull's eye effect.
The accent fell thereby on the first object. Not all the aesthetic requirements could be satisfied.
The glasses still showed some disturbing edge thickness, while the eye of the spectacle wearer in the field of view was perceived as reduced by the person standing directly facing the spectacle wearer.
Moreover the convexly-rounded transition between the flat edge and the concavely-hollowed center portion still remained too abrupt, which still had for the user a disturbing effect, as the usable field of view merged substantially without transition with the glass edge. Said transition and edge did remain an obstacle for the spectacle wearer.
The technique used according to said Patent did not moreover allow any inner torus-like grinding, which often made arranging the glasses in the frame difficult and was detrimental to the final aesthetic appearance of the spectacle.
Now all the myopes do not have the same need and do not bring the same requirements for an optimum field of view. Some myopes choose a more aesthetic spectacle glass, even then with some loss of field of view, while some other myopes still have no requirement regarding that field of view which is being considered as optimum for the normal myope. Every user of a spectacle-glass wants however as much as possible to have the disturbing refraction effect between field of view and edge be reduced.